Right now, all of our available material on Earth can be dig up in just about 2km below surface, basically just scratching surface. Just the surface, and it's enough to supplied and run our modern world. That mean way, waaay more material and resource, some even unheard of, could be found much, much deeper in the Earth itself.

Supposed that, someday, we will run out of material to dig, and not enough to recycle (Probably from us being a space civilization or something), drilling deep into the Earth would be both a nessesary, and a lucrative field which will guarantee some corporation a lifetime of wealth beyond their wildest dream right now. Supposed that, aside from asteroid mining, we also want to develop the Deep Drill Industry, tasked with mining precious ore from deep below, as depth far suppassed what we could do right now, what is the thing I should be worried about, what do you need, and what can you find beneath the crust? I would guess the molten, high-pressure mantle is certainly a thing to worried about, and probably most of the resource is in there, so we need basically high-temp liquid mining tool for it, and also a way to ensure a stable way up and down that wouldn't be disturb by continential movement.

(That's actually relevant to what I think, not an ad and it's a refreshingly ad-free app itself, but might not be obvious unless one has also gone past the "300 Adventures" bit.)

In slightly different terms, I remember digging moholes a lot when I used to mess with Minecraft. It's really not much more style over substance, but it kept me entertained. And that's without much difficulty¹ in engoneering terms.

I don't think (apart from in pure exploration/investigation) there's much need to start going all Journey To The Centre Of The Earth.

At best, we'll get a better idea about what deep veins there are that we can exploit using current deep-mining methods (perhaps extended a bit further than now). Or maybe, by 'fracking the mantle', we can develop a geothermal energy capability where no current capability exists, but I wouldn't want to be the one writing the Risk Assessments for a project. It may not be a huge problem, but it has potential to surprise us, so pick your spot well!

¹ Other than having to deal with creepers/etc (simple) and magma (also simple, but less so if you insist on collecting it all to carefully cast obsidian structures elsewhere back up on the surface) and my OCD need to store every lump of rock/etc in massed arrays of chests. One can be too obsessed, I decided, in Single-Player Survival Mode.

The only resource that is sufficiently scarce for this to make sense in the near future is oil. Oil can be extracted comparatively easily, since it is a fluid. For soild mining, it's difficult to imagine the mantle ever coming into play. There are some scarce solids (e.g. platinum, irridium, and natural ores rich in scandium and lanthanides), but mining them robotically from NEOs or even asteroids is probably more practical. In the extreme long term, hypothetically, even those sources could be depleted, but that is well beyond the scope of what can be meaningfully predicted.

If the main argument is an exhaustion of bulk "stuff" digging is going to beat drilling in all but specialized cases. The mining industry already does lots of open-pit extraction, because it is a lot safer and presumably cheaper. Not pretty, but obligatory remediation afterwards mitigates some of that. There's more waste material that needs to go somewhere, I imagine that can be a problem. That's a topic I could obtain more familiarity with.

Some shaft mines go down over a mile, so obviously it isn't always practical.

Platinum group metals from iron-nickel asteroids / NEOs are hopefully going to make a lot of neat stuff that relies on them as catalysts (like fuel cells) much cheaper. I'm glad to see that that process is finally getting beyond futuristic predictions and has some credible ventures starting to get funded. It could even be the motivation to get a more than half-assed space infrastructure going, now that would be something! (my favorite near-term beat-the-gravity-well (because LEO is halfwaytoanywhere!) technique is laserablation, but that's off-topic.)

Perfection is achieved, not when there is nothing more to add, but when there is nothing left to take away.-- Antoine de Saint-Exupery

p1t1o wrote:It is going to be a very long time before "get it from space" becomes the cheapest/easiest option for anything.

Not when there are gigatons of almost every element dissolved in the oceans just sitting right on the surface of the Earth.

Perhaps, but it will be far longer before extracting it from the mantle becomes the cheapest option. Also, you can't just extract whatever you want from seawater. What do you suppose the concentration of osmium in seawater is? How many tons of water would you need to process? Space may be expensive, but it isn't the most expensive.

andykhang wrote:I would guess the molten, high-pressure mantle is certainly a thing to worried about, and probably most of the resource is in there, so we need basically high-temp liquid mining tool for it, and also a way to ensure a stable way up and down that wouldn't be disturb by continential movement.

If you're talking about drilling into the mantle generally, you don't have to worry too much about the drift, because the outermost mantle is the lower part of the (rocky) lithosphere and they move together, so you'll only perceive continental drift as a 1cm/yr ocean current. If you want to drill all the way through to the (plasticky) asthenosphere, you've got a bigger job on anyway, depending where you are:

Those brown, red and orange areas along the divergent boundaries are freshly built and still crumbling, making standing on them a bad idea. The blue, indigo and violet areas are presumably more stable, but you've got the width of Ghana between surface and boundary under that Mali / Burkina Faso / Côte d'Ivoire area, with all sorts of issues associated with that:

Now iridium and tungsten melt somewhere above 2400°C and somewhere above 3400°C respectively, so you could hypothetically drill down through those temperatures and even through the 1300°C that Sydney Uni says you'd find at that boundary, and if you pump enough lubricant down that drill you can keep it cool enough for the lubricant to perform its job ... probably. I say "probably" because we use thicker oils for hotter applications and thinner oils for colder ones, and hydraulics set up for +20°C don't work too well at -20°C so you'd have issues with very viscous oil on its way in becoming near boiling where it's doing its job, and while the oil is effectively flowing through a heat exchanger to warm the inbound oil and cool the outbound oil and reduce this problem, you still need to push enough oil down the inside of the hole made by the drill and back up that same hole. I think this means a big drill, because fluids flow better down wider holes, but of course a bigger drill needs more oil. Ultimately, you'd have to slow down to avoid overheating.

Whatever heat difference between inbound and outbound fluid at the top of your shaft is left when you can't drill any further can be used to generate electricity, and if you give up on drilling you don't mind it boiling down there, but short of pulling the oiled drill out and putting an internally-insulated coaxial water pipe down in its place, I don't see how you'd reduce the effectiveness of a 400 km heat exchanger.

Eebster the Great wrote:The only resource that is sufficiently scarce for this to make sense in the near future is oil. Oil can be extracted comparatively easily, since it is a fluid. For soild mining, it's difficult to imagine the mantle ever coming into play.

That's an interesting image. Not least that the shoreline data in the image clearly shows a resolution of features far smaller than the entire islands obviously decided to exclude as 'too small to bother with'. (Primarily looking at the Danish peninsula and the English Channel shoreline of France, yet no British Isles, but also the Caribbean and US eastern seaboard. I have to imagine where Japan is, but at least the Koreas are still there to help me (and the nearby plate boundaries). And how about NZ?)

On a more practical level, I now wonder about the inland Ivory Coast and Burkina Faso-ish geology. I must check some topological and geological maps! (Then narrow down which, maybe Russian, location might be near that lone Eurasian purple pixel.)

Soupspoon wrote:On a more practical level, I now wonder about the inland Ivory Coast and Burkina Faso-ish geology. I must check some topological and geological maps! (Then narrow down which, maybe Russian, location might be near that lone Eurasian purple pixel.)

Looks like that purple spot is practically right underneath Moscow.

***

Coupla comments on the area around Burkina Faso & The Ivory Coast, why is that part interesting?

p1t1o wrote:Coupla comments on the area around Burkina Faso & The Ivory Coast, why is that part interesting?

The huge splash of purpleness, basically. It's not even anywhere near Wakanda, or else I could blame it on an exotic meteorite! Thicknesses of crust genarally happen away from the edges (obvious exceptions being near Japan, surprising but for its subduction nature, the area of Qatar (I think), a bit of the coastal Andes and surprisingly little extra thickness in the Himalayas) but that stands out against the not-that-thick centre of Africa, more than the other couple of 'random' thicker-than-yellow patches.

Was also half expecting to spot the Rift Valley, with a splosh of red between Nubian and Somali sub-plates where the future new African Ocean is due to emerge in some further tens of millions of years. Must be very localised to not already show graphable signs of the nascent 'mid-ocean ridge'. Especially given some of the depressions in that area (at least relative to the highlands they thread between).

But that's why I might be browsing some geological maps quite intensely, when I get the opportunity (and back off this stupid device with its small screen data allowance, aging battery and occasional glitches).

That's an interesting image. Not least that the shoreline data in the image clearly shows a resolution of features far smaller than the entire islands obviously decided to exclude as 'too small to bother with'. (Primarily looking at the Danish peninsula and the English Channel shoreline of France, yet no British Isles, but also the Caribbean and US eastern seaboard. I have to imagine where Japan is, but at least the Koreas are still there to help me (and the nearby plate boundaries). And how about NZ?)

On a more practical level, I now wonder about the inland Ivory Coast and Burkina Faso-ish geology. I must check some topological and geological maps! (Then narrow down which, maybe Russian, location might be near that lone Eurasian purple pixel.)

Good look finding Mt Etna on that map though, because they left off that part of Italy, along with Corsica, Sicily and Sardinia. I think the map may have been drawn in by someone who didn't care much and was just getting the vague idea there. The coastlines of Greece and Turkey have not been drawn accurately at all and they didn't try all that hard with the south end of South America, either. Possibly the most relevant omission of coastline is north of Australia, where there's a big blue patch that seems to be open ocean on the thickness map.

You'd think anyone into tectonic plates and their boundaries would be interested in the home region of Krakatoa.

I'm not seeing anything from Yamoussoukro to Nara that'd suggest a really think plate there from 2328 km up. The most interesting feature, to me, is at Payona. Several rivers, including the Niger, drain into a green area, which is drained by several small rivers that form the Niger. That suggests geology happened there a long time ago. Check out the striations, too. That IS a geological place. It isn't lined up one way or another with the contours of that enormous boobie on the underside of the plate, though. Given that the South Atlantic is a fracture line through a continent (and a lot of the bits of South America that don't fit are what rivers ahve washed out into that crack since it happened) the thick part in W Africa extended into S Africa, and is now between the Orinoco and São Fransisco rivers, with the Amazon washing right over it.

Eebster the Great wrote:The only resource that is sufficiently scarce for this to make sense in the near future is oil. Oil can be extracted comparatively easily, since it is a fluid. For soild mining, it's difficult to imagine the mantle ever coming into play.

Oil in the mantle? Isn't oil sort of limited to the crust?

Maybe! But if we found oil in the mantle, someone would eventually head down there to get it.

There are ideas that methane and some higher alkanes can form in the athenosphere and bubble up to the lithosphere, so it's not completely crazy. I don't know what the consensus is on the quantity of such "abiogenic" gas and oil though, so there might not be enough to matter.

Eebster the Great wrote:What do you suppose the concentration of osmium in seawater is? How many tons of water would you need to process?

A good question. Tons don't seem like the right unit to me, though. I went with cubic km of seawater per kg of Osmium. I got the concentration from here. There's a big uncertainty in the Osmium figure; the other trace elements are generally stated without a range. References to sources for the data are provided.

Ugly math spoilered. I might come back later and format it with LaTEX.It's set up so other substances can be substituted easily.

Wow. Well let's take the round figure of 100 km3/kg and say the world needs 200 kg/yr Os. So we would need to process 20,000 km3 of seawater annually or about 55 km3 per day. Even split between 100 processing plants, that's 550 million tons of water per plant per day. Doesn't really seem possible.

Thats still a collosal amount of water to process, but then Osmium is one of the rarer elements in seawater. Its one of the rarest on the planet.

I dont think Osmium is a great measure of mining technique to be honest, its a bit of an outlier in terms of abundance and demand.

At ~$13,000/kg and <100kg/ann production, the total market is only worth $1.3M or so.

Whether we mine the sea, the mantle or asteroids, Osmium will always be an added extra that will bring down the price, not a target for seeking deposits. Unless someone in the future comes up with a valuable use for many tons of osmium.

I was deliberately choosing osmium due to its rarity and low solubility. My point was that we can't just process seawater for all our mineral needs, and osmium is a rather dramatic example of that.

But gold is perfectly fine. There is a reason panning for gold was never an especially lucrative business. But if we are specifically talking about seawater, the concentration of gold is in the parts-per-trillion range. You would never be able to get enough gold out of the water to make it profitable, even if you could somehow separate it from everything else that is also in the water, typically at far higher concentrations.